1. Field of the Invention
The present invention concerns the precise end-to-end alignment of two optical waveguides formed independently and one of which is buried in a wafer such as a semiconductor wafer. A longitudinal lateral mark usually called the "hybridation mark" is used for this purpose.
2. Description of the Prior Art
The optical waveguides are of strip form and are referred to hereinafter as "optical strips". The problem of aligning them arises in particular when an amplifier waveguide has to be connected to an optical waveguide. The mark is usually a rectilinear flank recessed into the wafer. Its height is often different than that of the optical strip.
If two strips to be aligned are on the surface of a wafer (these are called "external" strips), the positions of the lateral channels on either side of the strips and of the valley at one lateral extremity defining the mark are etched into the same protective layer. Chemical etching or particle beam etching is then employed to recess the lateral channels of the strips and, to a very partial extent, the valley of the mark. The lateral channels and the strip are then protected, after which etching of the valley of the mark is completed.
Transposing this method to aligning a buried strip, the formation of which requires further epitaxial growth, is ruled out by the fact that the protection of the lateral channels of the optical strips degrades the wall of these channels which must be of good crystallographic quality at a later stage to constitute an interface for further epitaxial growth. It is impossible to restore this surface in the case of a laser strip element amplifier junction because the optical strips must have a narrow square cross-section. This cross-section must be formed between deep channels which rules out restoration to modify the shape of their cross-section.
Until now, the alignment mark for aligning a buried strip in a monocrystalline semiconductor wafer has been formed in a crystal plane. However, this method cannot be used in the case of hybridation in silicon Vees of strip semiconductor amplifiers inclined to the cleaved faces. In this case the alignment marks must be inclined to the cleaved faces.
The general object of the present invention is to obtain precise relative transverse positioning of two components that have to be etched independently, such as the flanks of an optical strip to be buried and an alignment mark, without crystallographic constraints, and in particular in such manner as to allow subsequent accurate end-to-end alignment of two optical strips one of which is buried.